Low-energy exchange reactions between hydrogen isotope mesoatoms

In terms of the Faddeev-Hahn equations in the two-level approximation the exchange reactions in low-energy hydrogen isotope mesoatom collisions for the total momentumL=0 have been considered. Elastic and inelastic cross-sections of the scattering channels as well as the rates of the exchange reactions for the (d+p) and (t+p) collisions have been calculated.     

Quadrupole moment and quadrupole relaxation of spin of muonium and mesoatoms

It is shown that muonium in the ground state has a quadrupole moment. Existence of the quadrupole moment of muonium leads to essential influence of crystal electric fields on the precession and relaxation of its spin in a medium.     

Model for milling of powders

A model is proposed for mechanical milling of powders that relates the applied energy to average particle size D in the powders. It is shown that the milling energy is consumed for the rupture of interatomic bonds in crystalline particles and for the creation of an additional surface during powder fragmentation. The appearance of microstrains ɛ retards powder fragmentation. Average particle size D after milling decreases with increasing milling time t and decreasing particle size in the initial powder or its mass M. The calculated results are compared to the experimental data obtained on a tungsten carbide WC powder.     

Model for Topological Fermions

 We introduce a model designed to describe charged particles as stable topological solitons of a field with values on the internal space S ³. These solitons behave like particles with relativistic properties like Lorentz contraction and velocity dependence of mass. This mass is defined by the energy of the soliton. In this sense this model is a generalization of the Sine-Gordon model¹(We do not chase the aim to give a four-dimensional generalization of Coleman’s isomorphism between the Sine-Gordon model and the Thirring model which was shown in 2-dimensional space-time) from 1 + 1-dimensions to 3 + 1-dimensions, from S ¹ to S ³. For large distances from the centre of solitons this model tends to a dual U(1)-theory with freely propagating electromagnetic waves. Already at the classical level it describes important effects, which usually have to be explained by quantum field theory, like particle-antiparticle annihilation and the running of the coupling. Received November 30, 1999; revised June 20, 2000; accepted for publication October 2, 2000     

A Model for Polyelectrolytes

We have solved a polymerizing version of the mean spherical approximation (MSA) for polyelectrolytes. The polyelectrolytes are modeled as tangentially bonded hard-sphere segments interacting via the Coulombic potential in a continuous medium with dielectric constant. Analytical solutions for thermodynamic properties and radial distribution functions at contact are obtained for some specific systems (negatively charged chains and counterions) studied in the literature via computer simulations, with which good agreement is found for the osmotic pressure.     

A Model for Neutrinos

Neutrinos are the weirdest of elementary particles, nearly massless and chiral. They oscillate between flavours, furthermore. We try to find a rationale for this maverick behaviour.     

Model for Thermal Oxidation of Silicon

Technical Physics - Nanometer-thick silicon oxide films are needed for miniaturization and increase in the working rate of electronic devices. Interpretation of the initial stages of silicon...     

An Improved Pinchoff Equivalent Circuit Model for Determining PHEMT Model Parameters for Millimeterwave Application

An improved equivalent circuit model under pinchoff condition for extracting parasitic model parameters for Double Heterojunction -doped PHEMTs is presented. Good prediction for S parameters and noise performance are obtained up to 40GHz. A modified parameter extraction technique based on this new model was use to determine a PHEMT equivalent circuit model. Signification improvements of the accuracy of S parameters are obtained by using the new pinchoff model.     

Interest-Driven Model for Human Dynamics

Empirical observations indicate that the interevent time distribution of human actions exhibits heavy-tailed features. The queuing model based on task priorities is to some extent successful in explaining the origin of such heavy tails, however, it cannot explain all the temporal statistics of human behavior especially for the daily entertainments. We propose an interest-driven model, which can reproduce the power-law distribution of interevent time. The exponent can be analytically obtained and is in good accordance with the simulations. This model well explains the observed relationship between activities and power-law exponents, as reported recently for web-based behavior and the instant message communications.     

Geometrical Model for Phenylthallium Dihalides

The geometry of the phenylthallium dihalides, PhTlX₂(X=F, Cl or Br) which has heitherto been unknown, has been proposed on the basis of several qualitative aspects and quantitative arguments. These molecules have a planar structure with C_2v symmetry and the ring geometry has been assumed to be the same as that of benzene. The ring-substituent bond length has been taken to be 2.218 A° in all the three molecules, and the Tl-F, Tl-Cl and Tl-Br bond lengths in respective molecules have been estimated to be 1.878, 2.366 and 2.520 A°. The remaining parameter inter-bond angle, F-Tl-F has been taken to be 116° in PhTlF₂, whereas, angles Cl-Tl-Cl and Br-Tl-Br in respective molecules have been taken to be 120°, as expected in the case of a pure sp² hybridization.     

A Model for Branch Competition

Branching (or tip-splitting) is a ubiquitous feature of growth processes in nature. We introduce a simple model, linear in growth probabilities, of branch competition that combines tip-splitting processes, local screening, and extinction of branches whose growth has come to an end. This model admits an exact solution; which is corroborated by numerical results. An extension of the model that depends quadratically upon growth probabilities exhibits a phase transition, with non-trivial scaling in the neighborhood of that transition.     

Model apparatus for quantum measurements

We present a model system that behaves as a measurement apparatus for quantum systems should. The device is macroscopic, it interacts with the microscopic system to be measured, and the results of that interaction affect the macroscopic device in a macroscopic, irreversible way. Everything is treated quantum mechanically: the apparatus is defined in terms of its (many) coordinates, the Hamiltonian is given, and time evolution follows Schrödinger's equation. It is proposed that this model be itself used as a laboratory for testing ideas on the measurement process.     

Model for cold dark matter

We present a model for cold dark matter based upon continuum bound states of thee ⁺ e ^– system. These continuum bound states, referred to as photonium states to distinguish them from the well-known bound states of positronium, are shown to have cross sections and lifetime properties consistent with abundant production in the early universe and survival to the present time. Thus photonium can easily account for more than 90% of the total mass of the universe.The authors have benefitted from discussions with Charles J. Benesh. This work was supported in part by the US DOE grant no. DE-FG02-87ER40371, Division of High Energy and Nuclear Physics and by contract no. W-7405-ENG-82.     

Model for current-driven edge-localized modes

Edge-localized modes (ELMs) are cyclic disturbances in the outer region of tokamak plasmas that are influential in determining present and future tokamak performance. In this Letter, we outline an approach to modeling ELMs in which we envisage toroidal peeling modes initiating a Taylor relaxation [Phys. Rev. Lett. 33, 1139 (1974)10.1103/PhysRevLett.33.1139] of a tokamak outer region plasma. Relaxation produces a peeling destabilizing flattened edge current profile and a stabilizing plasma-vacuum current sheet; the balance between the two determines the radial extent of the relaxed region. The model can be used to predict the energy losses due to an ELM and reproduces experimentally observed variations with edge safety factor and plasma collisionality. There is an intrinsic "deterministic scatter" in the model that also accords with observation.     

Model for spatial microtubule oscillations

Under particular in vitro conditions, oscillating spatial and temporal waves of assembled microtubules can be observed. A reaction-diffusion model is presented to reproduce these results. This model is based on a set of chemical reaction equations and extended to include spatial dependence and diffusion. The basic properties of the model are presented and the results are demonstrated to connect the observable waves with turbidimetric measurements. The results of the model are consistent with experimental findings.     

Transport Theory for Friedberg-Lee Model

By means of correlation density matrix theory and in terms of Wigner distribution function for quark, we obtain the transport equation for Friedberg-Lee model, which includes the coUision terms consis ten tly.     

A Markov Model for Kinesin

We investigate the validity of a Markov approach for the motility of kinesin. We show in detail how the various mechanochemical states and reaction rates that are experimentally measured, can be used to create a Markov-chain model. We compare the performance of this model to motility data and we find global similarities in the load and ATP-concentration dependency of speed and mean run length. We also discuss the relation between the experimentally found stalling behavior and thermodynamic expectations. Finally, the Markov chain modelling provides a way to calculate the mean entropy production and the (power) efficiency.